Dry kiln and in the art of kiln drying



May 28, 1940. J, F, OB

DRY KILN AND IN THE ART OF KILN DRYING 7 Sheets-Sheet 1 m m hw FiledJune 3, 1935 R INVENTOR.

y 1940. J. F. COBB DRY K ILN AND IN THE ART OF KILN DRYING Filed Jime s,19:55 7 Sheets-S het 2 Hm rlhn W INVm May 28, 1940. F, B 2,202,143

DRY KILN AND IN THE ART OF KILN DRYING Filed June 5, 1955 7 Sheet-Sheeta Q 0 Q I\ O a r F! p Ill .5533:

. I V Q INVENTOR.

May 28, 1940. J COBB 2,202,143

DRY KILN AND IN THE ART OF KILN DRYING Filed June 3, 1935 .7 SheetsSheet4 INVENTOR.

May 28, 1940. J. F. COBB 1m KILN AND I: THE ART OF KILN DRYING 7Sheets-Sheet 5 Filed June 3, 1935 '7 Sheets-Sheet 6 Filed June 3, 1935May 28, 1940.

MN I Nu m m V m May 28, 1940. J, F, OBB 2,202,143

DRY KILN AND IN THE ART OF KILN DRYING Filed June 5, 1935 7 Sheets-Sheet7 Patented May 28, 1940 DRY KILN AND in "ins and er nun parme JamesForrest Cobb, Portland, Greg. Application June 3, 1935, Serial Ne.24,655

10 Claims.

This invention relates to cross circulating drying kilns of thecharacter of that shown in my co-pending application, Serial No,492,026, filed October 29, 1930, of which this is a continuation in partand it has for its object to provide a kiln presenting marked featuresof advantage and improvement over the kilns oi the prior art and theirmethods of control and operation as will be more particularly pointedout in the detailed de- -scription which follows and succinctly definedin the appended claims.

In the accompanying drawings where my invention is illustrated inpreferred form of embodiment:

Figure I is a longitudinal vertical section of one form of embodiment o!my invention showing my heating system" and-air circulating systemwithin the kiln, with the fan ducts removed.

Figure II is a plan view of Figure I, but showing the fan ducts in placeand heating systems within the kiln.

Figure III is a transverse vertical section at IIIIII of Figure Ishowing the fan ducts and heating systems in place.

Figure IV is a transverse vertical section at the line IV-HV of FigureI.

Figure V illustrates a. modified form of Ian ducts having baiiieslocated within the fan ducts instead of on the corners of the fan ductwall.

Figure VI is a plan view of a modified form of embodiment of myinvention furnished with right and left hand fans opposed in pairs, andshowing my control system diagrammatically.

Figure VII is a longitudinal vertical section at VII-VII Figure VIshowing a modified form of my kiln illustrating a heating system at eachend and fans located above the stock-loads with fan ducts removed.

Figure VIII'is a transverse longitudinal section of a part of my kilnillustrating a modified form of heating system in operative relationshipto the fans, with fan ducts removed.

Figure IX is a view of another modification of my'invention in respectto the heating system in relation to the fans with fan ducts removed.

Figure X isa view' of my kiln illustrating another modified form ofheating system with fan ducts removed.

Figure XI illustrates diagrammatically a preferred form of embodiment ofmy heating systems.

Figure XII is a plan view 01' a -modified form of my invention showingfans above the stock-loads and in one corner of the kiln and a modifiedform of heating system.

Figure XIII is a vertical longitudinal section to it.

(ill. 34-46) taken through the tan ducts illustrated in Figure ml withthe heating system thereof superimposed thereon, in dotted lines anddiagrammati-' caily illustrating my control system.

Figure XIV illustrates a transverse vertical section XIV2QV of Figures mand m.

Figure XV illustrates a transverse vertical sec= tion at XV-XV oi FigureVI and VH.

Figure XVI is a detailed illustration of a dia= phragm valve detached.Figure XVII is a crosssection of one of my spray nipples illustrated inFigures I, m and IV. Figure XVIII is a plan viewoi nay-min illustratinga modified form 02 air circulation system with larger capacity fans atthe ends thereoi'.

Figure m is a longitudinal vertical section along the lines HX-W 01'Figure III Figure m is a cross section along thelines XX-XX of Figures mand m. 1

Referring to the numerals on the drawings, in each figure thereof wherethey appear, i' indicates opposite side walls of the M111, 2 the floor,3 the roof, and i the end walls defining a closed chamber andconstituting the outside walls of the kiln. Said wallsmay be of anysuitable and preferred material and construction, and are combined inany manner preferred so as to confine within the closed chamber or m thegaseous circulatory medium with the heat that is imparted The end walls,4, or at least one of them. are preferably made to include some form ofdoor by which material to be dried may be conveniently introduced intothe kiln and withdrawn from it.

Extending lengthwise through the kiln are tracks .or rails i which aresupported on the ground as in Figure XV or at suitable intervals withinthe kiln at desired elevation above the fioor 2 as by cross-beams 6. Thetracks are designed to support and carry wheeled trucks I. which may beof any usual form preferred, and which are united in pairs, preferablyby crossbeams or bunks 8 on which the lumber or other material to bedried is piled in the usual manner.

Suspended from the cross-beams 6 or extended above the beams 31 aresuitable hangers or sup ports which are preferred as means of supportfor the pipe. Separating the heating pipes are the pipe spacers whichhold the pipes separated so as to permit a free air flow across them.

The heating systems preferably consist of return pipe systems, as shownfor example in Figures I, II, VI and VII, the legs of each 01' which arejoined in units at top and bottom by the headers l3 and It and/or i4 andit, which aresupplied with steam from a source of supply notillustrated, as by means of supply pipes I! which are controllable as byautomatic diaphragm valves ll or 29 or hand controlvalves.

Each of the heating systems A and B consist of return pipes having twolegs, one above the other, the upper one 2| leading from the top orsupply header l3, and the lower one 22 leading into the bottom or drainheader IS vertically the kiln by L's 21 and a nipple 28. The L's 21 andthe nipples 28 or other suitable connections are used to permit theouter pipes 2| and 22 of the heating system A to lie in substantialparallelism and uniform proximity on the outside of the pipes 2| and 22in the inner system B on both legs of each system.

The heating systems, whether one or more, are located on one or moresides of the kiln as illustrated, or at suitable intervals, in case of amultiple track kiln which is contemplated by my invention. The heatingsystems are installed so that steam condensation will drain by gravity,as for example, from the top headers J3 and Il to the bottom headers l5and I6, through the return fittings at the opposite end of the heatingsystem, designated return joint end for convenience.

It is well known in the art that uniform distribution of heat andhumidity throughout the length of the kiln is essential in a charge kilnand that one of the functions of circulation is to distribute uniformlyheat and humidity conditions throughout the length of the kiln. Iaccomplish this by the arrangement and control of my fan, heating andhumidifying systems.

In the past, heating systems in internal fan kilns have not beendesigned with special consideration of the rapid loss in heatingcapacity of the steam as it travels within the pipes from one end of theheating system to the other. Consequently, the end of the kiln at whichthe steam enters has been the hottest end, which is an objectionabiecondition.

The use of temperature and humidity controls having bulbs, one of whichis indicated at 15 in Figure I, are well known and commonly used inkilns. The bulbs are usually located at the same end of the kiln atwhich the steam enters. The heating system aggravates the tendency for ahigher temperature at the end where the steam enters by raising thetemperature which automatically cuts off the steam supply to the heatingsystem when the temperature at the bulb reaches the setpoint. The fastcirculation produced by the fan system, in rapidly recirculating thekiln atmosphere across the pipes, quickly conveys the heat from the said,pipes to the temperature control bulb soon after the steam is turnedon. In many cases, when very little steam is required to maintain theset temperature, the automatic control instrument frequently turns thesteam on and then off the heating system before the steam can pass tothe opposite end of the heating system from which it enters.Consequently, the upper end of the kiln or that portion adjacent to thetop header end of the heatiglg system ishotter than other portions ofthe I overcome this objection by using a heating system of single ormultiple units each having a single return,so that the bottomheaders l5and/ or l6 are located just below and at the same portion of the kiln asthe top or supply headers l3 and I4, and by providing suflicient slopein the pipes to permit water of condensation to drain by gravity fromthe top to the bottom headers. This provides a space between the upperand lower legs of the heating system or systems at the steam feed orupper end of the kiln and provides very little space ,between the twolegs of each system at the opposite or lower end of the kiln.

In this manner the heating system is related to adjacent fans so that agreater volume of air is circulated across one leg at the header end' ofthe heating system than across the other leg, and air is circulatedacross both the legs substantially equally at the return joint end ofsaidsystern. By circulating less air across the header ends of both thelegs taken collectively than across the retum joint ends of said legs, Iam able to effect more uniform distribution of heat in the kiln.

By positioning the fans in overhead fan kilns (see Figures VII and XIX)so that their longitudinal axes are above the level of the top leg ofthe heating system, I am able to circulate substantially all the airacross the bottom leg of the heating system its full -length, and aportion only of the air across the supply header end of the top leg ofthe heating system, because of the vertical spacing of the headers. Atthe lower 'or return legs of the heating system because the pipes atthis end are located close together in the path of the circulatingatmosphere. In this way I am able to effect more uniform heatdistribution in an overhead fan kiln.

By dividing the heating system into multiple units, two units on eachside as illustrated in Figures I and II, and by reducing the amount ofheating surface within the kiln to a practical minimum, the steam whenturned on will pass fromend to end of each or either system before. thetemperature within the kiln is raised to the set point, controlled bythe thermostatic temperature control bulbs, aforesaid.

Two heating systems may be divided longitudinally with one heatingsystem 64 at one end of the kiln and another heating system 66 at theother end of the kiln as illustrated in Figures VII, XIII and XIX. Thesame relationship described above between the heating system andadjacent fans applies to each.

For producing kiln atmospheric circulation, I prefer to usesubstantially such means as are commonly known as the internal fan crosscirculation system. In such a system a series of reversible rotary fans3| are mounted, preferably,

. wall l constituting in effect a closure on that I side for thecompartment to which it is appropriated, the side of the compartmentopposite each solid well being open.

The solid walls di when employed are, disposed,

respectively, in succession on alternate-sides ofthe fan so as to dividethe series of compartments into units or fan ducts of which eachalternate one is open on one side and closed on the other side. By thedisposition just described of the several walls 39, so, and as, theresult is in their assemblage, to impart to the wall so constitutedthroughout its entire length what is designated as a zigzag wall oreffect.

The angle at which the walls 39 meet the walls ii, as shown in FiguresII, IV, and V1, is an obtuse angle on the fan side, but it is obviousthat the angle may be'varied, if desired, as in some instances it may be(see for example Figure II). Each of the walls last named is planted onthe bottom'fi of the kiln, or if overhead fans are used, in contact withair-tight closure means assembled, on their upper side, with the ceilingor root 3. The fanducts are completed by a floor M which is laid incontact with air tight closure on the top of the walls 39, 60, and M,when the fans are below the loads, and are attached to the bottoms ofsaid walls in like manher when the fans are above the stock-loads.

I prefer to use a series of right hand fans at one end of the kiln and'aseries of leftv hand fans at the opposite end, the zigzag wall beingreversed in direction at a medial portion of the kiln as shown in FigureII to provide cross circulation from one side to the other the fulllength of the kiln, in which case in the intermediate compartment whereright and left hand fans face each other, two fans will blow againsteach other in counter-acting currents in one di-' rection of circulationand withdraw atmosphere from the same compartment in the reversedirection of circulation as shown in Figure II.

The employment of right and left hand fans opposed in pairs distributedthe full length of the kiln so that each pair of fans may dischargecounteracting currents one against the other in either direction ofrotation illustrated in Figure VI, affords a feasible method ofcirculation, and can be used to embody'my invention.

In any embodiment of my invention, I may provide means for elfectingmore circulation of air in the end sections of the kiln which would beotherwiseits coolest sections. This may be accomplished by the use ofsimplebafiies as illustrated in Figures II,III, V, XII, and XIII orusing larger capacity fans in the end section of the kiln as illustratedin Figures XII and XIX.

Referring to Figure III, I' show baiiies, and 45, the baflies 44 beingrelatively narrower than the bafiles 45 because the latter must beprepotent and to reverse the circulatory currents and direct themtowards the ends of the kiln when the fan circulation is directedagainst them. On reversal of circ ulation, the baffles 44 would bebrought into efiectlve use. They need be relatively narrower than thebaiiies 55 because the air from the fans being in such case-directlydriven towards the ends of the-kiln, their function is accomplished bydirecting the air partially 1 transversely and, at the same time,allowing a certain amount of directional flow towards the ends, due tothe direct action of the fans.

Upon reversal of the fans the transverse air circulation of the kiln isreversed and the longitudinal circuit of air circulation at each end isalso reversed. Each-circuit of longitudinal air circulation at each endis also reversed.- Each circuit of longitudinal air circulation movesfrom the center portion of the kiln towards one of the two ends in onedirection of fan rotation, and upon reversal of fan rotation eachlongitudnal circuit is reversed and moves toward one end from the middleportion of the kiln on the opposite side of the stock loads from thesideon which it moved, before the fans were reversed.

It will be understood that the bafiles ,M and d5 are preferably set withpermanent flexure so that they may be made by adjustment to direct asmuch additional movement of atmosphere towards the ends of the kiln asmay be effective to prevent those ends from becoming too low intemperature and too high in humidity. On the contrary, it is madepossible upon occasion, to reduce the temperature and raise the humidityat the ends of the kiln by reducing the air flow toward the ends of thekiln or by reducing the amount of circulation at the ends of the kiln.

Referring to Figure II, it will be noted that the bellies 44 aredisposed in series at opposite ends on one side of the kiln, and thebaiiles 45 are disposed in series at opposite ends on the other sldeofthe kiln. 1

In Figures XII, H11 and XIV, the baflles 44 and 65 are shown as locatedon adjacent sides on1y of the fans, inasmuch as the fans are lofiexureto. guide and distribute the impinging circulating medium within thekiln.

It is desired to set thesewing baiiles so that the air of circulationfrom the fans 3! will be mainly transverse in course but will'havej aslight directional flow towards the respective .-,ends of the kiln whereI prefer to direct additional heated air from the fans 3!, to replacecooler air at the doors where it has lost tional air flow sets uplongitudinal recirculation toward the doors from the medial portion onone side thereof and toward the part of the kiln remote from the doorson the opposite side of the kiln.

It is to be understood that-the fans may be located above as .well asbelow the stock-loads of material to be dried. 'In'this case, therelative disposition of the heating system to the heat. This direcfansalready described above, is maintained. In some cases the fans may belocated in one corner of the kiln, as shown in Figure XIV. In that case,the heating system may be in two multiple units of pipes instead ofthree or four as illustrated in other figures.

Their primary function being to direct the air from the fans to thenormally cooler parts of the kiln, they may be located at the corners ofthe ducts in Figure '11 or midwise of the duct, as in Figure V, or theymay be omitted all together when right and left hand fans are used inseries atopposite end of the kiln.

In my kiln, I prefer to provide fresh air conduits 46 and 41 havingopenings 49 and 50 respectively at each fan for the intake of outside oratmospheric air into the kiln. In the case of overhead fans, ventilatorsmay be substituted for said conduits, and will perform the doublepurpose of fresh air intake and of exhaust from the kiln.

The fresh air conduits 46 and 41 are provided, respectively, with freshair doors 52 and 53, which may be opened at will to let fresh air intothe respective conduits 46 and 41. The

air conduits may have openings 49 and 50 provided with covers 56. Saidcovers are preferably sliding doors and can be used, respectively, to

cover all or part of the openings 49 and 50 so that the fresh air intakeat each fan is adjustable in such manner as to provide a desired mediumof fresh air to each fan. Preferably only, one fresh air conduit 46 or41 will be used at a time. The one on the suction side of the fans willbe lused and the door 52 or 53 of the opposite side will be closed,depending upon the directioniof circulation of the fans, consideringthat the fans are reversible. I alsoprovide ventilators 51 in the roofof the kiln which may be opened at will to ventilate excess moisturefrom' the kiln.

There are several modifications of my heating system illustrated inFigures VIII, IX, and X,

which give the same relationship of effective radiating surface to aircirculation as that shown in Figure I. In these illustrations, part ofthe air circulated is permitted to bypass part of the heating pipes ofthe heating system at the end of the system at which the steam enters.At the lower end or return leg end of the system, a substantiallygreater volume of the air is passed in operative communication with thepipes of both legs of the heating system.

The amount of air bypassing the heating units varies in difierent crosssections of the kiln; but the closer to the point of feeding steam, therelatively greater the amount of air that is bypassed; and the closer tothe return leg ends of the heating system, the greater the volume of.kiln atmosphere that is circulated across the pipes. This relationshipof volume of air passing across the pipes to the heating emciency of thepipes is maintained. The numerals of Figure XI are applicable to theheating systems of Figures VII, VIII, IX, X, and XIX. In Figures VIII,IX, X,

and XI the heating systems illustrated are on ures II, VI, and XII.

A particular feature of my kiln is the method of control of temperatureand humidity therein illustrated diagrammatically in Figures VI, VIII,XII, and XIII. I preferably employ any well known instrument for thecontrol of temperature and/or humidity for example, that described inPatent No. 1,624,887 issued to E. H. Bristol, April 12, 1927. The wetcontrol bulb 12 having a water box 15 and wick 18 and the dry controlbulb 13, both at the same end and same side of the kiln are a part ofindividual or separate controllers, and control the wet and dry bulbtemperatures at that end by actuating diaphragm valves 11 and 16 on thespray and heating systems 58 and 64, respectively. The dry control bulb83 at the opposite end of the kiln controls the dry bulb temperature atthat end by actuating the diaphragm valve 86, controlling the heatingsystem 66 at that end of the kiln.

I have discovered that the wet bulb temperature, in an enclosed dry kilnhaving substantially the same amount of fresh air intake and ventilationoutlet at the two ends is substantially constant. Thus, by controllingthe dry bulb temperature at each of the two ends, I am able to efiecttemperature and humidity control at the two ends and substantiallythroughout-the kiln.

I preferably'provide dual dry bulbs on each of the dry bulb tube systemsat each end of the kiln with one bulb thereof on each side of thestockload at each end of the kiln to give control of the air enteringthe said stock-load in either direction of transverse air circulation.Two dry bulbs, for example, 83 and 83A are connected by capillary tubes14 or 84 and are connected by a capillary 1| or 8| for example, to oneactuating element such as a helical coil IS in the instrument of PatentNo. 1,624,887. When dual dry bulbs are used, the bulb in the hottest airactuates the helical coil of the instrument through effecting the highervapor pressure therein.

The control system in my kiln is particularly suitable for drying stockwhich varies in initial moisture content. Diflerent loads of material vvary in initial moisture content, and because of this variationthere isdifficulty in maintaining uniform drying conditions throughout thelength of the kiln. Stock having higher moisture content requires moreheat to maintain a drying temperature under given conditions ofcirculation than does stock having a lower moisture content. My controlsystem makes it possible to maintain uniform drying conditions ofhumidity and temperature throughout the kiln by furnishing additionalheat when and where needed regardless of the variation of moisturecontent of the stock in the kiln. Although moisture content of the stockdoes or does not vary at the two ends of my kiln and the amount ofmoisture evaporated from the stock does or -does not vary at the twoends of the kiln, I am able to effect control of the temperature andhumidity of the entering air at the two ends of the kiln by using aseparate heating system and a dry bulb control thereof at each end ofthe kiln and a humidifying means therein and a wet bulb control thereofat one end.

2,202,148 This principle applies to my kiln operated progressively aswell as charge system. For example, in a progressive kiln, when greenlumber is put into the kiln every day at the green end uniformlydistributed circulation, a control of,

the dry bulb temperature at each end, and a wet bulb control at one end,to give independent control of the temperature and humidity at each endofthe kiln.

Reference is made to my co-pending appiica-'.

In Figures XVIII, XIX, and XX, I illustrate a different form of aircirculating system with fans turned at right angles to the longitudinalaxis of the kiln. The fans 90 are driven in any suitable above. Theeffective relationship of the air cirfollows; The kiln, being chargedwith material manner, for example, by individual motors 9|, which arereversible in rotation and which circulate air across heating systems 84and 66 on one side of the fans and heating system 2l-22 extending thefull length of the kiln described culation to the heating systems isexactly the same as when other designs of air circulating systems areused. The fans 90 are preferably of the same size and rotated at thesame speed and give uniform air fiow transversely within the kiln. Theend fa'ns 90A and 90B are preferably of larger capacity to provide morecirculation at the ends of the kiln.

The heating systems 64 and 66 also may have extended surface radiationatthe'ends of the kilnto provide a greater heating effect to counteractheat losses through the ends of the kiln.

The operation of mykiln is substantially as to be dried and the doors,if more than one, closed, the fans are set in motion and t e an matictemperature and humidity-controls, wellknown in the art, are set for agiven schedule of temperature and humidity at each end of the kiln.Steam is supplied to one of the heating systems to give sufilcientradiating surface to permit a rapid flow of steam from the top to thebottom header. The rapid transverse or cross circulation of air cooledby drying contact with the stock to be dried and then passing across thepipes in transverse circuits condenses a considerhowever, by passing agreater amount of the circulating medium across all the pipes of one legand a greater amount of air across the other leg at the return bend endthereof than across the header end thereof, whereby a greater uniformityof the heating of the kiln results.

The baifies when used are set so as to deflect the. greater amount ofcirculation towards the ends of the kiln or regions which are naturallyrelatively cooler and higher in humidity, due to heat losses as throughthe doors. By adjusting the baflies in the manner already indicated, a

midity. By the control of For example a drop Figure II)-.

can be obtained. A similar adjustment of .the extending latdirection ofthe spray nipples 60 teraliy from the spray pipe 68, having a cap 62 andperforated holes 6i as illustrated inFigure XVII, produces a uniformdistribution of huthe supply of steam to the heating coils at the twoends, the adiustment of the directional flow of the circulating medium,and the adjustment of the direction of and the supply ofsteam to thespray nipples, I

be usedat one end, may be used at the such case, it would pensatingfactors to increase the radiation at the lower end of the kiln. This maybe accomplished by using greater surface radiation, such as additionalor fin pipe at the'lower end of the heating system to compensate for theless effectiveness of the heating system at that region (see.Compensation could also be made for less radiation at any point in thekiln by use of larger fans or of fans having a greater angle of bladewhich would permit them to discharge more air across the stock loads andthe heating system at the end sections of the kiln or other sectionswhere the capacity of the drying atmosphere may be less (see FigureXIX). In fact, extended by amplified surface radiation, the use oflarger fans, or fans having a greater angle of blades may be used at anypoints in the kiln or to increase the drying effect of the circulatingatmosphere in lieu of the arrangement described above. 1

The principle of my invention contemplating means for compensating forgreater heat and humidity losses at the ends of a kiln, for example, maybe employed in ki ns having distributed fans operatively mounted ontransverse shafts as well as on longitudinal shafts (see Figure XX). Inany case, greater heating surface at the ends of the kiln, adjustment ofhumidity spray discharge pipes to supply drier steamat the ends of thekiln and wetter steam in the intermediate section, or the use of largerfans or fans having a greater angle of blade to circuate a greatervolume of air at the ends of the kiln, may be used to accomplish thedesired result. I prefer to employ any or all ofthese means operatingindividually or simultaneously to uniform drying conditions within thekiln.

When fans on transverse shafts are used, I prefer to use right hand fansatone end and left hand fans at the oppositeend of the kiln installed sothat the efiective direction of discharge of right hand fans will betoward the end of the kiln at which they are located, and the effectivebe necessary to use com-- f provide more direction of the left hand fanswill be toward their end of the kiln. In this manner greater heatingeffect is attained at the two ends of the kiln, or whatever coolerregions thereof may exist towards which they may be respectively made todischarge.

It is understood that this invention is not limited to the exact designand form illustrated and described. Modifications of the structures andmethods herein described and equivalents are self-evident to thoseskilled in the art; therefore,

more uniform distribution of heat and humidity it is to be understoodthat the invention includes within its scope whatever changes fairlycome within either the terms or the spirit of the appended claims.

Having described my invention, what I claim 1. In a dry kiln, means forefiecting reversible cross circulation therein, heating means therein atone end, heating means therein at the other end, humidifying means insaid kiln, a dry bulb controller having thermostatic bulbs at one'endfor controlling the heat supplied to the heating means at that end, adry bulb controller having a thermostatic bulb at the other end forcontrolling the heat supplied to said heating means at that end, asingle wet bulb control in said kiln for the actuation of saidhumidifying means, whereby the temperature and humidity are controlledat each end of said kiln, and means for controlling the temperature ofthe kiln atmosphere before it enters the load comprising dual dry bulbson one of said dry bulb controllers, one of said dual bulbs being in thepath of circulation as atmosphere moves froma heating means to a load ineach direction of air circulation.

2. In a cross circulation dry kiln having stock loads therein, a heatingsystem at one end, a heating system at the other end, a humidifyingsystem in said kiln, a dry bulb controller having a thermostatic bulb atone end, for controlling the heat supplied to the heating system at thatend, a dry'bulb controller having a thermostatic bulb at the other endof said kiln for controlling the heat supplied to said heating system atthat end,

. a dual dry bulb for each of said dry bulb controllers, each on theopposite side of adjacent loads from the said dry bulbs, a wet bulbcontrol having a thermostatic wet bulb in said kiln for actuating thehumidifying system, whereby the temperature and humidity of entering airare controlled at each end of said kiln.

3. In an overhead fan dry kiln having uniformly distributed ventilationtherein, the combination with, a series of reversible fans operativelymounted and distributed in substantial alignment, substantially the fulllength of the kiln, for effecting cross circulation across stock loadstherein, two return coil heating systems comprising top andbottomheaders, and top and bottom legs connected respectively thereto, saidheaders being vertically spaced apart at one end of said heating system,said legs converging, and being connected by a return joint at itsopposite end, whereby said headers may be supplied with steam anddrained respectively, one of said r heating systems being at one end ofsaid kiln and the other being at the opposite end, each of said heatingsystems being so related to the adjacent fans that a greater volume ofair is circulated across one leg than across the otherleg, and more airis circulated across the return joint end than across the header endscollectively of said legs, a dry bulb controller for each of saidheating systems, each controller being provided with dual dry bulbs, onebulb of each controller being located in the path of circulation asatmosphere moves from a heating system to a stock load in one directionof circulation, and

the other bulb being located in the path of circulation as atmospheremoves from said heating system to a stock load in the other direction ofcirculation, thereby controlling the temperature of the kiln atmospherebefore it enters the load at each end of the kiln in each direction ofair circulation.

4. In a dry kiln having fans distributed therein heat supplied to saidheating means at the other end, a single wet bulb controller having athermostatic wet bulb in said kiln for the actuation of said humidifyingmeans, whereby the temperature and humidity are controlled at each endof said kiln, and means for controlling the temperature of the kilnatmosphere before it enters the load comprising dual dry bulbs on one ofsaid dry bulb controllers, one of said dual bulbs being in the path ofcirculation as atmosphere moves from a heating means to a load in bothdirections of air circulation.

5. In a dry kiln of the reversible cross circulation type, for a stockload therein, air circulation means, atmosphere heating means andcontrol means for said'heating means, said control means beingcharacterized by dual bulb apparatus, one bulb of which is located inthe path of air circulation on each side of the heating means, one ofsaid bulbs being in the path of circulation of kilnatmosphere as itmoves from theheating means to pass across an adjacent stock load, andthe other bulb being in the path of circulation of atmosphere as itmoves from an adjacent load to pass across the heating means, said bulbsbeing jointly connected to the operative control means, whereby theactuation of said control means is automatically taken over by the bulbin the position having the highest temperature. 4

6. In a dry kiln having a seriesof reversible fans operatively mountedand distributed in substantial alignment the full length of the kiln,the combination of two return coil heating systems comprising top andbottom headers, and top and bottom legs connected respectively thereto,said headers of each system being vertically spaced apart at one 0ndthereof, said legs of each system converging and being connected by areturn bend at its opposite end, said headers being supplied with steamand drained respectively, one of said heating systems being at one endof said kiln and the other being at the opposite end thereof, each ofsaid heating systems being so related to the adjacent fans that agreater volume of air is circulated across one leg than across the otherleg thereof, and more air is circulated across the return bend end thanacross the header end of the leg across which a lesser volume of air iscirculated, a dry bulb controller having thermostatic bulbs in the pathof air circulation at one end of said kiln for controlling the heatsupplied to the heating system at that end, a dry bulb controller havinga 'thermostatic bulb at the other end of said kiln for controlling theheat supplied to said heating system at that end, humidifying means insaid kiln, a single wet bulb controller having the thermostat located atone selected position in the kiln whereby, temperature and humidity arecontrolled throughout the kiln, and means for controlling thetemperature of the kiln atmosphere before it enters the load'comprisingdual dry bulbs on one of said dry bulb controllers, one

of said dual bulbs being in the path of circula- 7 tion as atmospheremoves from a heating system to a load at one end of the kiln in bothdirections of air circulation.

r '7. The method of controlling the temperatur and humidity ofatmosphere before it enters stock loads distributed throughout akiln,which consists of circulating atmosphere transversely across saidstock loads therein, of reversing the circulation at time intervals ofheating the atmosphere at each end of the kiln before it circulatesacross the stock loads, of determining the dry bulb temperature of theatmosphere immediately before it enters the stock loads in eitherdirection of circulation, 'of controlling'the heat added to theatmosphere in response to variations in the dry bulb temperature and inhumidifying the atmosphere in response to variations in the wet bulbtemperature-at but one end of said kiln, whereby more uniformly driedstock is obtained.

8. In a cross circulation dry-kiln having stock loads therein, a heatingmeans at one end, a heating means at the other end, a humidifying sprayin said kiln, means for reversing the direction of air circulation inthe kiln, a dry bulb controller for controlling the heat supplied to theheating means at the one end, a dry bulb controller for controlling theheat supplied to the heating means at the other end, dual dry bulbapparatus for each of said-dry bulb controllers, each bulb of whichbeing located in an atmospheric space between a heating coil and a stockload, one of said dual bulbs for ,each controller being in the path ofcirculation of kiln atmosphere which moves from the heating means acrossan adjacent stock load, and the other bulb for each controller being inthe path of circula-' tion of the atmosphere which moves from anadjacent load across heating means, a wet bulb control having athermostatic wet bulb in said kiln for actuating the humidifying spray,where by the temperature and humidity of the kiln atmosphere before itenters, a stock load are controlled at each end oi said kiln.

atively connected to each of said controllers,

.cally taken over by the bulb in the position hav- 9. In a dry'kilnhaving thereinstock varying in moisture content, a substantiallyuniformly distributed transverse reversible air circulating meanstherein, a steam spray extending substantially the full length of thekiln for supplying I heat and moisture the full length of. the kiln, awet bulb temperature control having a thermostatic bulb in said kiln forsaid spray, an individual heating means at each end of the kiln, and adry bulb temperature controller at each- 10 end of the kiln for theindividual heating means, dual dry bulb apparatus for each of said drybulb controllers one bulb of which being located on the entering airside of a stock load between the heating means and the load, andthe-other bulb of which being located between the stock load and theheating means on the leaving air side of the load, said dual dry bulbsbeing operwhereby actuation of said controller is automatiing thehighest temperature.

10. In a dry kiln of the reversible cross circulation type, aircirculation means, atmosphere heating means of the return coil typelocated and 25 steam fed at one end of the kiln, a separate atmosphereheating means of the return coil type with a supply header located andsteam fed at the other end of the kiln, and control means for each ofsaid heating means characterized by dual 80 bulb apparatus so disposedwith respect to the heating means that one bulb is on one side .of theload and the other bulb is on the opposite side and each is in the pathof circulation after the circulated atmosphere has passed across the Iheating means in either direction of atmosphere circulation, the saidbulbs being operatively connected to the control means, wherebyactuation of each of said controllers is automatically taken over by theone of its bulbs in the position having 40 the highest temperature.

JAMES FORREST coma.

